The communications industry is rapidly changing to adjust to emerging technologies and ever increasing customer demand. This customer demand for new applications and increased performance of existing applications is driving communications network and system providers to employ networks and systems having greater speed and capacity (e.g., greater bandwidth). In trying to achieve these goals, a common approach taken by many communications providers is to use packet switching technology.
Consumers and designers of these systems typically desire high reliability and increased performance at a reasonable price. As non-blocking packet switching fabrics are typically expensive and non-scalable to large packet switching systems, many packet switching fabrics are designed such that internal congestion might arise depending on traffic loads and patterns. It is important for packet switching systems that can have internal congestion to handle the congestion in some manner, such as using buffers and generating and communicating flow control information (e.g., XON, XOFF signals) to sending sources so they can decrease the traffic load and allow the congestion to subside. However, known methods of reacting to flow controls signals can lead to poor traffic throughput, such as that produced by a synchronized on and off oscillation of sending sources.
For example, in a typical switching fabric, it is possible for certain destination ports to be oversubscribed. This creates a bottleneck where traffic becomes backlogged behind the congestion point. The backpressure threshold must be set low enough so that congested traffic does not occupy so many buffers that starvation can occur on other unrelated destinations. The peak occupancy is then dependent on the aggregate ingress traffic rate to that destination as there is a delay in the backpressure feedback loop where the occupancy can overshoot the threshold. Another problem that can occur is if the occupancy drains too quickly before traffic can be resumed. This can cause underrun and effective loss of speedup through the fabric. Moreover, the traffic can have a variable number of sources, yielding a very wide range in offered load. Known systems and methods do not adequately react to traffic conditions. Needed are new methods and apparatus for reacting to flow control signals by traffic sources.